Speed differential detecting means



Feb. 19, 1946.

C. D. STEWART SPEED DIFFERENTIAL DETECTING MEANS Original Filed April 1, 1942 INVENTOR CARLTON D. STEWART BY PM ATTORNEY Patented Feb. 19, 1946 UN FEED EPATENT 'OF'FIGE SPEED? DIFFERENTIAL DETECTING "MEANS Carlton DLstewartg wilkinsburg; Pa a'ssignorito I. The westinghouse Air Brake Company, Wilmmerdingy :Pa., a. corporation ofPennsylvania -1942; Serial No; 444,777

3 Glaims.

.Thlsinvention .relates .to speed. differential de- ..tecting...means and has particular relation to .meansfor detecting a difierence inthe rotational speeds of two. rotaryielements; suchastwo wheels -or wheelahd axle. units iof arailway carpfor a .Idesir'ed purpose; the .presentapplication being a wdivisionj of .my priorcopendin gapplication Serial No, 437,170, filedeApril 1}1942, and-assigned to j; the. same .assigneeas' the present application.

withoutreducing in speed -to alock'ed condition "and sliding.

" 'I'he'wheelsandaxles'of railway car'sandt-rains are constantly subject to severe shock-andvihra- ,t tlon duringtravel of the car or "train along the "rails'ofthe"trackdue to rail joints; rail unevenness and other causes. It is essential "therefore thatmechanism directly associated with andresponsive to the'rotative-condition of a wheel 'or Various types of. devices; both mechanical and lWwheel" andaxle umtbe 'siifiiciently 'sturdy ahd electrical in nature,..are. knownland. have. been serviceable'so as towith'stand the constant-shock employed for" detecting differences in themotarand vibration to whicliitis'su j .tional speedsof tworotary-elements for a, desired "It" is cco d y an j t y p es l indicatingor control. purposesuchas niaintainvention to provide apparatus whlch i associated ,ing a synchronous, conditionpf .thelrotary elel5"'directly"with the" wheels orwheet and axle asments. In thecase nirailwayicarsmand trains, sembliesof railwaypars and trainsforthe'purapparatus isrknown and has beenproposed where- D detecting "t pp g 7 Condition oft-he jby to'detect.thedifferencein therotational speed ""wheels" by acomparison or the speed of a slip- Of a slippingand aenon-slippingwheel orwheel P g' Whee1"andthat a; npp W unit whereby the .brakesassociated with theslipwhich apparatus is capable of withstanding' the ,Lpip wheel...unit.may. .be suitably controlled. soda continued shock and vibration on the wheel or vvvto preventsliding thereof. wheel units incidental to travel along the-"rails As. is wellknown; the exertion of a .braklnglefw qu t s i an" s t al q r feet on a vehicle. wheel. sutficienttoexceedrthe for ay c limit. .of adhesion between the .wheel .and'eroad' More specifically,itis'andbiecvofmyinvention surface or rail causes. the wh'eelto deceleratelat ...an abnormally. rapid rate-to. a. locked orrnon- .rotative -co'n'clitioniand. slide. Sliding of wheels is lobjectionable, particularly in. the (case .of railway car wheels," because sliding develops Yfiat spots necessitating. repair orreplacement rofthe wheels. 'MoreovenJ the braking reflect lonl the .vehicle. exl .ertedlthroiigh a sliding Wheel isumfich less than I that of a wheel which continuesto. roll.

Q As .distinct ..from .the term :fisliding, thetterm -slipping .or fslipping condition {of a wheelrretiers ate the rotation of e a wheel. at a speed .different from a peed corresponding to .vehiclespeed at. a; given-instant. .A slipping condition of a vehicle wheimayheiproducecl by. theapplication .Toi excessivebrakingiorce which causes. the wheel to decelerate toward a locked .condition,.in which rcasethe wheel rotates eat a. speedlessnthan a speed corresponding. to 7 vehicle: speed. 2011 r the .other hand, a wheel: mayislip in response .toethe application of excessive :propulsionv-torque;:in which case the wheelmrotates at a-efastenspeed than aspeed corresponding 'to' .veh'icle speed.

1111; .hasxbeen demonstrated, that if the degree t..bf 'applicatiomof the brakes associated-with a 'whee'lithat. begins to slip: is rapidly and promptly reduceiithe wheel will promptlycease to deceler- "ate :and iatfonce accelerate at a rapid rate *back :toward atspeedeorrespomd-ing. to vehiclespeed to 'pr0vide 'speed' differentialdetecting'means adapted to be associated with'railwaycar'whels "or wheel units and characterized 'by -rela'tively light weight commutator devices and associated *r'contacfielements whereby to'secure a'measure of the "rotationarspeed"of the-*-corresponding Wheels or wheel units. I

*Itis another'object' of'my invention toprovide *apparatus suited for' association with any "two rotary "elements; thespeeds of which it" iswle- "F'sired 'to' compare; which'apparatusjs -'characterized by an arrangement for detecting the "dif- "ference between the'rotati'onal speed ofone' trotary element and that of a sec'ond'rotary-"element whether the speed of-the saidone rotary element is'greater'cr less than-that ofthe second'rotary element.

" The above objects; and other objectsofmyin- "ventionwhich' will bemade apparent hereinafter,

are attainedjby an' illustrative embodiment thereof shownin thesin'gle figure of the accompanying drawing.

Description While the speed differentialdetettingappa- 0f fluid pressure brakes on ara-ilway 'car o'r train.

In order to understand my invention and its uses, therefore, it will be necessary to describe briefly the nature of the fluid pressure brake control equipment.

In the drawing a simplified brake control equipment of the well-known straight-air type is shown in connection with a single car having two wheel trucks II and I2, respectively, located at opposite ends of the car. Each wheel truck, the structural details of which are omitted, comprises two wheel and axle units or assemblies, each unit having a pair of wheels l3 fixed at opposite ends of a connecting axle [4.

The brakes associated with the car wheels 3 may be of any suitable type such as the conventional clasp arranged shoes engaging the rim of the wheels and applied and released in response to the supply and the release respectively of fluid under pressure to one or more brake cylinders l5, two brake cylinders being illustratively shown for each wheel truck. In the case of one wheel truck, illustrated as the wheel truck |2, one of the brake cylinders is of smaller diameter than the other so that the braking effort exerted in response to a given fluid pressure in all the brake cylinders is less on the wheel unit with which the smaller brake cylinder is associated than on the other wheels or wheel units. The wheel unit with which the smaller brake cylinder is associated will accordingly hereinafter be referred to as the underbraked wheel unit. The reason for providing an underbraked wheel unit will be explained hereinafter.

The apparatus whereby fluid under pressure is supplied to the brake cylinders l5 and released therefrom may comprise a so-called control pipe ll, a reservoir i8 which is normally charged to a certain pressure such as one-hundred pounds per square inch by a fluid compressor not shown, a manually operated brake valve IQ of the selflapping type, and a plurality of branch pipes Hu and Ill) respectively connecting the control pipe H to the brake cylinders of wheel trucks H and I2, in each of which branch pipes a magnet valve device 2| is interposed for a purpose presently explained.

Brake valve I9 is of the well-known type described in detail and claimed in Patent 2,042,112 of Ewing K. Lynn and Rankin J. Bush and is therefore shown only in outline form and will here be but briefly described.

Brake valve i9 comprises a suitable self-lapping valve mechanism having a rotary operating shaft to which an operating handle |9a is fixed. In the normal or brake release position of the brake valve handle ISa, fluid under" pressure is exhausted from the control pipe H to atmosphere through an exhaust port and pipe at the brake valve. Upon displacement of the brake valve handle in a horizontal plane out of its brake release position into its so-called application zone, the exhaust communication just mentioned is closed and a supply communication is established through which fluid under pressure is supplied from the reservoir l8 to the control pipe H. The nature of the self-lapping valve mechanism of the brake valve I9 is such that the pressure established in the control pipe H is substantially proportional to the degree of displacement of the brake valve handle out of its brake release position. The valve mechanism of the brake valve 9, moreover, possesses a pressure-maintaining feature for maintaining a pressure in the control pipe i1 corresponding to the position of the brake valve handle in the event that the pressure in the control pipe tends to reduce for any reason, such as leakage.

Each magnet valve device 2| is of a conventional double beat type having a double beat valve 23 which is urged into an upper seated position by a coil spring 24 and actuated to a lower seated position against the force of the spring 24 in response to energization of a magnet winding or solenoid 25.

In its upper seated position, the double beat valve 23 establishes communication from control pipe |l through the corresponding branch pipe Ila or llb to the corresponding brake cylinders l5. In its lower seated position, the double beat valve 23 closes communication through the corresponding branch pipe and establishes communication through which fluid under pressure is vented at a rapid rate from the corresponding brake cylinders through an exhaust port 25 in the magnet valve.

Thus, as long as the magnet winding 25 of each magnet valve device 2| is deenergized, the pressure in the corresponding brake cylinders I5 may be increased and decreased under the control of the operator in accordance with the increase or decrease of pressure in the control pipe net valve 2| is energized, the fluid under pressure in the corresponding brake cylinders I5 is rapidly vented to atmosphere through the exhaust port 26 independently of the pressure in the control pipe H.

A pressure responsive switch device 28 is also provided and is connected by a branch pipe Ilc to the control pipe I! so as to be responsive to the pressure in the control pipe.

Pressure switch 28 is preferably of a snap-acting type, such as shown in Patent 2,096,492 to Ellis E. Hewitt. Briefly, the pressure switch 28 comprises a pair of stationary insulated contacts a: and a movable contact 1 As long as the pressure in the control pipe is less than a certain low value, such as five pounds per square inch, the movable contact 1/ is actuated to its open position out of engagement with the associated contacts as. When the pressure in the control pipe I! increases above flve pounds per square inch, the contact 1 is actuated by snap-action into a. closed position engaging the associated contacts :0 and remains thereafter in such position as long as the control pipe pressure exceeds five pounds per square inch. When the pressure in the control pipe again reduces below five pounds per square inch, the contact y is actuated by snap-action to open position out of engagement with the contacts 2:. The purpose of. the pressure switch 28 will be made apparent hereinafter.

According to my present invention, I further provide wheel-slip detecting apparatus of the speed differential type for the purpose of controlling the magnet valve devices 2| in a manner to cause rapid venting of fluid under pressure from the brake cylinders in response to the occurrence of a slipping condition of the wheels of the corresponding truck.

The wheel-slip detecting apparatus which I provide comprises a commutator device 3| for each wheel unit, each commutator device being driven according to the rotational speed of the corresponding wheel unit in any suitable manner, as for example, by mounting it directly on the end of the axle within the journal casing in the manner indicated in the drawing. In addition, the wheel-slip detecting apparatus further When the magnet winding 25 of each mag- :momprises a transformer :3 2; zaniinductance-device ::;or:chokecoil Z3 3; andv axiull-wave rectifier: 34-ior reach wheel nmit: :Moreover; asrelayi 535: is intther :upnovidedi for :each wheeliunitexcept the; under- :braked' wheel-:unit.

if The commutator 5 devices" 3 l1. mayra'beyioinany suitable construction. :xAsrshown; theyzcomprise a plurality. of 'contactssegments' :31 suitably-securedrin?spacedrelationrzin a ring 38'qof'tinsulatrringimate-rial which isxin turnisecured to:thezend 'of. thetaxleiof a wheehinitdorzan 'extensiornithere- 3 of. Although I have ifor simplicityhhowvrndnly 1: six'icontact :segments" :'3 llnforsreaclr commutator, it will be :understoodthatz-in practice any desired number; may be employed- .DIBfBIQbIYIm'OIGfJlh'aH Eachofrthetransformers .32 comprises a-;pritrnary. windingizptand asecondary winding 32s. 'Each of the primary windings 232p fisurrranged to be alternately:"connectedrrto'and disconnected from a pair of bus fwires=4 l :and 42 :at arfrequency proportional to the rotationalspeed of the :corresponding wheel unit under the control of.::the corresponding commutator device 3l.: For-:this purpose, a'pairs'of brushes :43 is suitably mounted in: insulated fixed relationwithin'theaxle 'jour- 1ml of each wheel unit TfOl successive asimultaneous engagement with the commutator contact segments .31. "Each commutator device 3i and the associatedlpair of brushes 43 accordingly'form a; switch I device which isv connected in seriesirelation with the.corresponding'primaryrwinding 32p across the buswires' 4l1and 42 to"-falternate1y make and breakithe circuit "as the commutator device 3l "rotates.

Thebus wires :4l"and 42 areenergizeduby a suitable sourceof direct-current; suchias a storage battery 45; underthe control-r the -pressure switch 28. As'shown, the-bus wire "4 I is connected by a branch: wire *46 including the contacts 'of the pressure switch-2&to'fthe positive terminal of the battery 45- only whenzthe movable contact y of thepressure switch isrin its closed positionengaging the contacts as. The bus wire 42 1s constantly connected by a wire '41 to the negative terminal ofthesbattery '45.

Assuming that the pressureswitch nais closed and that the voltageof the --battery-45- is impressed across the bus wi-res 4l-- and 42', it will be seen that the-primary windi-ng npor each transformer 32 is alternately energized and deenergized 'at a frequencyproportionalto the rotational speed of the correspondingwheelnnit.

The alternating voltage that is inducedin the secondary winding 32s of 'each "transformer" 32 due to't'he" alternate 'energization and deenergization of each corresponding primary'winding 3217 will not remain uniform in efiective or'root mean square value over theentire range of operatingspeeds but such variation thereof'as does occur will not-"be" materially adverse "in effect with respect to the'ultimate'res'ult' that ibis-desired to obtain. The frequency of the alternating voltage inducedhineach "ofthe'secon'darywindings' 32s will, however;'varyinproportion'tothe the voltageinducedin the. secondary winding 32s of the corresponding. transformer. is "impressed, and two output terminals'fromwhich the rectifled direct-current voltage is supplied.

An inductance device. oriichoke coil 133v is. interposed between one terminal of the secondary errand a.sirigle;front eontactc.

:.I%hei windings b of: the relays 35 arezconnected in parallel relation 1 across, a" pairzof bus wires 5 I and ,ihwhich rare-in: turnrespectively connected :-:-to rthe: positive rand negative output terminals of 1 011 the :rectifier 34. "sassociatedwith the ,underbraked .1: wheeh unitm. condensei'. ;53.-. is connected across :zntheroutput terminalsnf :the'rectifier 13.4 associated r with lathe;1:unde-rbraked: wheel; unit :tin :xorder, to i:;sm ootlr";out:thelripple in 'the rectified or directlo :zcurre'nt: supjpliedtfrom the rectifier.

TMfIhewinding afofa eachiof the .EI'GIELYS 35' is ;con- :1: ne'otedrinsserieszrelationrwith, a' suitable zrsistor 55 across theioutput terminals ofrthe correspond- Zing rectifier-:34; a:suitabletncondenseriJ53nbeing I ::connectedracr0ss: the outputtot'terininals ot-reach zrecizifier' :342f0r; smoothing" out theripples ml the 3: directcurrent output :ofi the ::re ctifier.

The. arrangementfof thei'apparatus above .de- .gsc'ri'bed isxsuchzthat thewinding a 1of-each=relay i' 251cris-energized by a current which is substantially :z inversely proportional: to "the rotational: speed of -=.x:the corresponding "wheel unit over a; wide:range, ssuchaszfifteenmiles per hour to eighty=or ninety "smiles per hour, :and. that: the winding b for .each

.130 -re1ay':35vis energized by a current which iSlSllbstantiallyinverselyproportional to the rotational speed-of the underbraked wheel unit over. a; corresponding 1 speed range.

The direction-'01 flow of current "throughczthe 3 & windings wand 11 'of .each'relay 35-is suchtthat f the s windings 1': exert opposing: "magnetomotive forces, as indicated: by. the: oppositely: directed zzarrow heads On the; windings.

The resistors 55 are so deSlgI18d:iaS=t0 adjust the.current in thewindings d'jtO; a value iwhich "is substantially-'equal:ttoithat in the winding b ..und er normal conditions when all-wheels=are 'rotating at the'same speed.

L i Itwill be apparentthat; the' current energizing 5 "the windings a and b of theirelays'35 issubstantially inversely proportional: towthe-rotational speed of the corresponding wheel unitover ithB wide rangespecifi'ed above by reason'of the variation ofthe impedance 'of the inductance devices -33, in: the alternating current: circuit connecting the secondary winding- 32s of each"transformer to the input terminals of the rectifier 34,-with variationdnf the 'frequency of the alternating current.

In view "of theiact that the impedance ofthe "inductance devices or'choke coils 33-varies substantially in: direct proportion to the frequency of the alternating current flowing'therethrough, "and also in view ofthe fact that such variation oi the voltage supplied from the transformer 0 impressed on the input terminals fof .each rectijfier 34 will increaseeasl the {speed lot .the .corresnonding.v .wheel .unit decreasesover such. wide 7 range of operating speeds. The voltage produced at the. output terminals Jofeach rectifier 34 will thus vary correspondingly. Accordingly, since the current in the output circuit of each rectifier varies directly with the output voltage of the rectifier it will be seen that the windings a and b of the relay 35 are energized by a current varying substantially inversely with the rotational speed of the corresponding wheel unit over the wide speed range specified above.

By reason of the fact that the windings b of the relay 35 are energized over the wide speed range specified above by a current substantially inversely proportional to the rotational speed of the underbraked wheel unit, it will be seen that the windings b are continuously energized during such time by a current which is substantially inversely proportional to the actual speed of the vehicle. Such is the case because the underbraked wheel unit is never braked sufliciently to cause a slipping condition thereof.

On the other hand, over the operating speed range specified above, the winding a of each relay 35 is energized by a current which is substantially inversely proportional to the rotational speed of a corresponding wheel unit which may slip during a brake application. Accordingly, it will be seen that as long as each of the braked wheel units rotates at a speed substantially identical to that of the underbraked wheel unit the two windings a and b of each relay will exert substantially equal and opposite magnetomotive forces and consequently the contact of the relay will remain in its dropped-out position.

When one of the braked wheel units begins to slip, however, the current in the winding a of the corresponding relay 35 instantly increases at a faster rate than the rate of increase of current in the winding b due to the relatively rapid rate of deceleration of the slipping wheels with respect to the rate of deceleration of the underbraked wheel unit.

When a suflicient differential between the rotational speed of a slipping wheel unit and that of the underbraked wheel unit occurs, the ma netomotive force exerted by the winding a of the corresponding relay predominates over that exerted by the windin b of the corresponding relay and causes the contact 0 of the relay to be actuated to its picked-up position. As long as a slipping wheel unit rotates at a speed more than a certain amount below that of the underbraked wheel unit, the contact or the relay 35 corresponding to the slipping wheel unit remains in its picked-up position.

The contacts 0 of the two relays 35 for wheel truck II are connected in parallel relation in a circuit including the winding 25 of the magnet valve device 2| for wheeltruck I I so as to severally control energization and deenergization of the magnet winding 25.

In a similar manner, the contact 0 of relay 35 for the single braked wheel unit of wheel truck I2 is connected in series relation with the winding of the magnet valve device 2| for wheel truck I2 to control energization and deenergization thereof. The circuits of the magnet winding 25 of the two magnet valve devices 2| are sufliciently apparent in the drawing so that specific tracing of the circuits is deemed unnecessary.

Operation Let it be assumed that the car having the equipment shown in the drawing is traveling under power with the brake valve handle ISa in its brake release position so that the brakes associated with the wheels I3 are released and that the operator desires to bring the car to a stop.

To do so he first shuts oil the propulsion power in the usual manner and then shifts the brake valve handle I9a out of its brake release position into its application zone an amount corresponding to the desired degree of brake application. Control pipe I! and brake cylinders I5 are thus charged to a corresponding pressure and the brakes are applied on the wheels to a corresponding degree. At the same time the contacts of pressure switch 28 are actuated to closed position to cause energization of the bus wires 4| and 42. Thus current is supplied to the primary windings 32p of all the transformers 32 on the car only when the brakes are applied. The windings of the relays 35 are thus energized in substantially inverse relation to the speed of the corresponding wheel units as previously described.

As long as the wheels on the vehicle do not slip, no variation of the pressure in the brake cylinders I5 occurs except in accordance with variations of the pressure in the control pipe IT as efiected under the control of the operator by means of the brake valve I9. If, however, at the time an application 01' the brakes is initiated or at any time during a brake application, one or more of the braked wheel units other than the underbraked wheel unit begins to slip, a further operation occurs which will now be described.

Let it be assumed that the wheels of the lefthand wheel unit of truck II begin to slip while the brakes are applied. In such case, the contact 0 of the corresponding relay 35 is picked-up causing energization of the magnet winding 25 of the magnet valve device 2| of wheel truck The magnet valve device 2| is accordingly operated to close communication through the branch pipe Ila to the brake cylinders I5 of wheel truck II and also to cause fluid under pressure to be rapidly vented from these brake cylinders.

The venting of fluid under pressure from the brake cylinders l5 of wheel truck I I causes a correspondingly rapid reduction in the degree of ap' plication of the brakes associated with the wheel units of truck II and consequently the wheels of the slipping wheel unit promptly cease to deceler ate and begin to accelerate back toward a speed corresponding to vehicle speed without reducing in speed to a locked condition.

As previously indicated, the contact c of a relay 35 remains in its picked-up position until the slipping wheel unit rotates at a speed less than a certain amount below that of the underbraked wheel unit. Consequently the magnet valve 2i continues to effect the venting of fluid under pres sure from the brake cylinders I5 until the slipping wheel unit is restored substantially to ve hicle speed, thus insuring the restoration of a slipping wheel unit to vehicle speed.

It will be understood that the degree of reduction of the pressure in the brake cylinders will vary depending upon the initial pressure in the brake cylinders at the time slipping of the wheel units begins as well as adhesion conditions be tween the Wheel and rail or road surface. In any event, if a slipping wheel unit is not promptly restored substantially to vehicle speed, the venting of fluid under pressure from the corresponding brake cylinders continues. Thus, it is possible that the fluid under pressure in the brake cylinders may be completely vented or only partially vented depending upon the rapidity with which the slipping wheels are restored to vehicle speed.

When the slipping wheel unit approaches sufficiently close in speed to the rotational speed of aacaaoas the .mnderbrakedlwheel 'uniizithe magnetomotlve: s forces exerted:- by:-the1windings: .-a and b Ofi thi relay 35 corresponding:v to the slipping; wheel :unit: :1 again abecome 1 substantiallyz lbalanced 5:and-.. .the 1. contactsc of therrelayu35aiszthus restored toeits: droppedaout positionr;.The'magnet windingof the magnet valve; devices 2 |fOI.WhG8l. truck .I ris thus deenergized: and: the magnet valve :device restoredtoits .i-normali' condition. cutting oifxth'ei-aexh'austiav communication: from :the brake cylinders and. re.-=-.1 establishing .;the:; supply- .communicationzthereto: from the controlpipe l|;through the correspond-r ing. branch pipe .I Ia-1.

Fluid underzpressure is thusresupplied-to the brake cylinders l 5: of: wheel truck; 21 I to cause :re"-;. 1 applicationsof: the. brakes. athereong'the degreeaoi J application: :of :the brakes'rrestored corresponding tothe; degreeof pressure-established in ethecon trol pipe II. It will baapparent that duelto'thez pply;ofpnuidunderrpressure to the lbrakezcylinders.-:I 5 onvthe .wheel. truckihaving. the, slipping. wheelzunits theppressure instheucontrolpiperfl: tends to: reduce-1n HDWfiVI,'.='dl1&: to .the pressure-. maintaining: ieature: oiethelbrakewalve. .i 9', siiuid undenpressune: is 1 automatically supplied tonthe V COHtYOlvIJiDB. lltOUCOXHDGHBfl'tfitfOY-thG' fluidzsupapliedrto; the .brake: cylinders-so: that-the pressure 1' in the controlpipenremains atj'ga .value :corresponding to the position; of; the 'brakervalvehandlen If, upon reapplication wot-the :brakes. on wheel truckv 21 I: inthe, .mannergiust; described; theisamey wheehunit. OlgthBaObhfiltWhBCLllllit begins tosslipy. the above operation isrrepwted'sothat at ndtime. are; wheels permittedwto 1. deeelerate: :toxa locked conditionsand slide.- 3

In the-event that. the cbrakedwqvvheel; unit a of? wheeltruclr- .l 2: other thanthe underpraked:whdel r. unit begins. to slip during; a brakecapplicationgtheu corresponding relay ;35r:is rpicked-up to; causeop-x; eration of. the corresponding-magnet valvedevicemi 2 l to; vent: fluid under pressure: from. the brake: 5- cylinders forsthatztruck-and a subsequent'rres supply of: fluid-under pressurethereto when-zthevs: slipping. WhB1 runit is restored --substantia1ly to; the vehicle speed; This operation is :identical to .1 that; described. for: the left-handlwheelr unit of: wheel. truck rI I; and. is (accordingly. not-repeated: in detail...

When the car comes-to a complete. stop: insirevsponseto the application of the brakes,- relays 5 are alwaysrestoredsto: their dropped-out position? because of thecessation of. snpplyof current tort thewindings. a anchb thereof; Accordingly; the magnet valve .devices 2|: are always restored to. their normal positions whemthetcarcomes tor-:8. complete stop and-thusathe. brakes'are always; applied-onthe canwhen-thexcar comes to a complete stop as long as pressure is maintained in the control pipe l1.

When the operator desires to again start the car, he must, therefore, first release the brakes by restoring the brake valve handle l9a to its brake release position in which fluid under pressure is exhausted from control pipe I l and the connected brake cylinders I5 to atmosphere through the exhaust port and pipe 20 at the brake valve.

Upon the reduction of the pressure in the control pipe I! below five pounds per square inch, the contact 3/ of the pressure switch 28 is restored to its open position, thereby deenergizing the bus wires 4| and 42 and consequently any of the primary windings 32p that may happen to remain connected across the bus wires through the corresponding commutator device 3| and assooiated brushesflz; In: this connection; it willbe apparent:that= thetcprimarywindings 32p :of the transformers should be so designed as not to over.- heat during :continuous. een'ergization -:occurring while the cards .st0pl1ed'.with, the brakes. applied or, ilIl'.'the alternative, isuitable ithermall-y respon.-'- sivcs Glitz-Out :switches: should be provided-forum.- 1 terruptingnthe circuit eof the individual'iprimarv windingsyszp; The pressure: switch ;2 8== also interzru-pts a the circuit for t the @magnetuwindings 2 5' of, the magnet valvedevicesgil therebysinsuring' tieenergizatlon" thereof.

Itiwill..be'understood that while .I have shown i thegequipment'comprisingmyinvention:as applied.- .only to a .single:car,;suoh equipment Inay'beemployedon: each cargoft-a train; In the case of a train.- :of';ca.r.S;-' it' is preferable to provide, :ingwellwl known manner; suitable magnet-valves on-each can-electrically: controlled through train 'wiresbyy:

a master controllereon one car,- such as the loco-v motive at the @head-end ofthe train,- for efieeting simultaneous variations .of' pr essure throughout.- the length of the control pipe 1 I l. t

It. will; be apparent that'while I have described my speed-differential detecting apparatus par. ticularlyinconneetion with a brake-control equip-g ment-whereinit detects :the rotation of-a brakedwheel-aura speed more than-a certain amount. less' than. that of the underbraked wheel onwheel.

..unit,. the apparatus is nevertheless suited for and:

mayfiunctionto detect the rotation of a wheel at a .speed; more than a :certain. amount higher than. that. of the lunderbraked .wheel ,or wheel unit, assuming. that the battery circuit is l closed, as.by a suitablycontrolled switchparalleling the switch 28. Such rotation of a wheelmight occur on railway. cars where .thewheels are driven. by propulsionmotors. Itlwillbe apparent .thatthe application .of propulsion torque. to the wheelsto a degree. sufiicientto exceed the-limitfoiadhesion betweenthe Wheels and the rails willv causev the wheelsitolslipor race, thatis,.rotate at a speed, higherthan the speed of the non-slipping or undefrbraked wheel.

In this situation, the contactsiof the relays 35.1 are picked-up in responseto the racing of the .ve.-, hiclei wheels, that is the, rotation thereof atfia speed higher than the speed ofthe .underbraked wheel. Itwillfbe understood that in the case of propulsion, the underbraked wheel may be a wheel "which isnot subjectto propulsion torque so that it-willalways"rotate at a speed corresponding -to-*vehicle speed;

It will 1 be apparent that since the currents in the windingsa andb -of-the relays 35-are substantially inversely: proportional to the rotational speeds of the'ucorresponding wheel units,- the current in the winding a of the relays will be reduced sufficiently below that of the current in the winding b of the relays so the contact of the relays is actuated to its picked-up position due to the predominating eifect of the current energizing the winding 2) of the relay. This is just the opposite of what occurs when the wheels slip during braking because in such case the winding a of the relay 35 exerts a predominating eifect over the winding b.

While I have not shown any means associated with the relay 35 whereby the propulsion motors associated with driving wheels of a car may be controlled in response to the operation of the relays 35, such apparatus is well known. Moreover, such apparatus is not a part of my present invention which concerns the speed diiferential detecting apparatus per se.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Apparatus for detecting a predetermined differential in the rotational speeds of two rotary elements, said apparatus comprising a relay having two separate windings, means for supplying an alternating current voltage having a frequency substantially proportional to the rotational speed of one of said rotary elements, means for supplying an alternating current voltage having a frequency substantially proportional to the rotational speed of the other of said rotary elements, means for impressing a direct-current voltage on one winding of said relay which voltage is substantially inversely proportional to the frequency of the alternating current voltage supplied by the alternating current voltage supply means associated with said one rotary element, means for impressing a direct-current voltage on the other winding of said relay which voltage varies substantially inversely with the frequency of the voltage supplied by the alternating current voltage supply means associated with the said other rotary element, said windings being effective to exert substantially equal and opposite magnetomotive forces as long as the rotational speeds of the two rotary elements do not difier by more than a certain differential, one of said windings being effective to exert a magnetomotive force sufliciently predominating over that exerted by the other winding to cause pick-up of the relay only when the corresponding rotary element rotates at a speed less than that of the other rotary element by an amount exceeding said certain differential.

2. Apparatus for detecting a predetermined differential in the rotational speeds of two rotary elements, said apparatus comprising a relay having two separate windings, a first source for supplying an alternating current voltage having a frequency substantially proportional to the rotational speed of one of said rotary elements, a second source for supplying an alternating current voltage having a frequency substantially proportional to the rotational speed of the other of said rotary elements, a full-wave rectifier for each of said alternating current voltage sources, an inductance device for each of said rotary elements, the alternating current voltage source for each rotary element being associatively connected to the corresponding rectifier and inductance device in such a manner as to cause the rectifier to supply a direct-current voltage substantially inversely proportional to the rotational speed of the corresponding rotary element, the

output voltage of the rectifier associated with said one rotary element being impressed on one winding of said relay and the output voltage of the rectifier associated with the other rotary element being impressed on the other winding of said relay whereby said windings are energized respectively by direct-current substantially inversely proportional to the rotational speed of the corresponding rotary element, said two windings exerting substantially equal and opposite magnetomotive forces as long as the rotational speeds of the two rotary elements do not differ by more than a certain amount and one of said windings being effective to exert a magnetomotive force sufficiently predominant over that exerted by the other winding to cause pick-up of the relay when the corresponding rotary element rotates at a speed more than a certain amount less than that of the other rotary element.

3. Apparatus for detecting a predetermined differential in the rotational speeds of two rotary elements, said apparatus comprising a source of direct-current, a transformer for each of said rotary elements having a primary winding and a secondary winding, a switch device associated with each rotary element effective to alternately connect the primary winding of the corresponding transformer to said direct-current source and disconnect it therefrom at a frequency proportional to the rotational speed of the corresponding rotary element, a full-wave rectifier for each rotary element having a pair of input terminals and a pair of output terminals, an inductance device for each of said rotary elements, the secondary winding of each of the transformers being connected across the input terminals of the corresponding rectifier in series relation with the corresponding inductance device, the arrangement being such that the direct-current voltage produced at the output terminals of each rectifier is substantially inversely proportional to the rotational speed of the corresponding rotary element, a relay having two separate windings one of which is subject to the output voltage of one of said rectifiers and the other of which is subject to the output voltage of the other of said rectifiers, said two windings exerting substantially equal and opposite magnetomotive forces as long as the two rotary elements rotate at substantially the same speed and one of said windings being effective to exert a magnetomotive force sufiiciently predominant over that exerted by the other winding to cause pick-up of the relay only when the corresponding rotary element rotates at a speed more than a certain amount less than that of the other rotary element.

CARLTON D. S'I'EWART. 

